Third generation partnership project (3GPP) and Long Term Evolution (LTE) mobile telecommunication systems provide high data rate, lower latency and improved system performances. Handover procedure is intended to reduce the interruption time and it is an important function for the overall system performance. The handover procedure can be between base stations of the same Radio Access Technologies (RAT) or between different RATs (inter-RAT). When a handover event occurred, the radio resource is at first released in the serving radio network and then established in the target radio network. Therefore, the connection to the source is broken before or during the connection to the target is made. For a user equipment (UE) which has an ongoing session, the delay caused by the handover procedure causes a temporary service interruption if the ongoing service is a latency sensitive application. Longer interruption time will result in an unexpected service termination.
To minimize the service interruption time during the handover procedure, the UE should establish the radio resource in the target radio network as quickly as possible and remain in the connected-state. In addition, once the UE has successfully acquired the radio resource in the target radio network, the UE shall avoid unnecessary connection release; otherwise, the UE needs to perform reestablishment to regain the service. The extra reestablish procedures result in not only user experience degradation but also being considered as a waste of radio resource.
This invention describes a method to minimize the service interruption by avoiding unnecessary connection release during underlying radio network switching.